Can We Quantify the Quality of Dialysis? Looking Beyond Kt/V

In the United States, dialysis outcomes have been notoriously poor, especially in comparison to outcomes in Japan and certain European countries. Indeed, this was one of the main reasons behind the establishment of the Dialysis Outcomes & Practice Patterns Study (DOPPS). Unfortunately, there has been little progress in reducing this international inequality. This led to the formation of the Kidney Care Quality Alliance, with the goal of establishing better quality metrics. One of those is the ultrafiltration rate (UFR) threshold of less than 13mL/kg/hour. This was endorsed by the National Quality Forum; however, it was not included in this year’s final rule by the Centers for Medicare & Medicaid Services on reporting for performance. In an NKF-KDOQI (National Kidney Foundation–Kidney Disease Outcomes Quality Initiative) controversies report, Kramer and colleagues discuss the history of dialysis prescription, the evidence behind this threshold, and the controversy behind its implementation.

Fig 1 (bottom) from Kramer et al AJKD, © National Kidney Foundation | Data from the Dialysis Outcomes and Practice Patterns Survey (

Fig 1 (bottom) from Kramer et al AJKD, © National Kidney Foundation | Data from the Dialysis Outcomes and Practice Patterns Survey (


The Evidence

The Hemodialysis (HEMO) Study, which demonstrated no benefit for increasing Kt/V or high flux membranes, reported in a secondary analysis that cardiovascular and all-cause mortality rose sharply with UFR 10 to 14 mL/kg/h compared to less than 10 mL/kg/h. Notably, patients on the higher UFRs also received a significantly lower treatment time. Similar results were reported by a prospective Italian study (threshold > 12.4 mL/kg/h) and in a DOPPS trial. But is the numerator (UF) or the denominator (time) more important? Let’s step back and look at the first ever trial in dialysis, the National Cooperative Dialysis Study. This study randomized 151 patients to two different treatment times (2.5 to 3.5 hours or 4.5 to 5 hours) along with different timed average urea concentrations. The difference between the two treatment times approached significance (P = 0.06), but this was subsequently overshadowed by the Kt/V analysis. Until recently, with the advent of nocturnal dialysis and the staggeringly impressive results from the Tassin group and others, treatment time has not been a focus, which has been reflected in guidelines throughout the years (see table).

Guideline Year Comment on Treatment Time
NKF-DOQI 1997 No consensus on time
ERBP 2002 Minimum 3 sessions/wk of 4h each; increase time/frequency if hemodynamic instability (grade B)
CARI 2005 No recommendation possible; the relationship between hours of dialysis per week and survival requires further exploration
KDOQI 2006 Minimum of 3h/session or 9h/wk (if low residual function, <2mL/min)
Canadian Society of Nephrology 2006 No time threshold; consider time as a factor if suboptimal adequacy (URR < 65%)
UK Renal Association 2013 Minimum frequency 3×/wk, session length 4h (grade 1B)
KDOQI 2015 Minimum of 3 h/session or 9 h/wk (if low residual function, <2mL/min; grade 1D)

Abbreviations: ERBP, European Renal Best Practice; CARI, Caring for Australians with Renal Impairment; KDOQI, Kidney Disease Outcomes Quality Initiative; NKF-DOQI, National Kidney Foundation­–Dialysis Outcomes Quality Initiative; URR, urea reduction ratio.

Unintended Consequences

The challenges of creating guidelines and performance measures are always the unintended consequences. This issue is discussed at length in the report from Kramer et al. It is important to consider how facilities could reduce UFR to the desired limit of 13 mL/kg/h or less. One could focus on the probable root cause, interdialytic weight gain, which is, unfortunately, notoriously unamenable to a quick fix. The most common suggestion, restricting fluid intake, is mostly unhelpful, and a focus on the more useful sodium restriction is harder to execute given the limited access to healthy foods for most dialysis populations. Increasing dialysis session time is faced by resistance from patients, and dialysis units are constrained by the availability of shifts and time, as well as the cost burden. This leads to how this measure could be gamed: setting a higher than actual dry weight is an easy route (Is the denominator weight to be based on actual, dry, or ideal body weight?). Other pitfalls include more cramps and symptoms with attempts to fulfill the measure, which could lower patient satisfaction, another metric. In addition, such an arbitrary threshold would bias against units with a high proportion of older women and frail and elderly patients, who have a lower weight and easily cross the 13 mL/kg/h threshold. Not surprisingly, a majority (54%) of the 1,090 respondents to a KDOQI survey answered “No” to a question on limiting UFR based on an arbitrary threshold.

More Evidence in the Works

Two ongoing trials may shed more light on this vexing question. The Pragmatic Trial of Hemodialysis Session Duration (TiME) is a cluster-randomized controlled trial comparing usual care to 4.25 hours three times per week, with mortality, hospitalization, and quality of life as outcomes. A Clinical Trial of Intensive Dialysis (ACTIVE) compared 24 hours of dialysis therapy per week to the standard in the participating countries (Australia, China, Canada, and New Zealand) of 12 to 18 hours for 12 months.

The current review by Kramer et al provides a valuable service by laying out the evidence, historical context, and possible implementation problems for having a UFR threshold in an extremely clear and articulate review.

Swapnil Hiremath, MD
AJKD Blog contributor

To view the article abstract or full-text (subscription required), please visit

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